The present invention relates to an electrode for medical applications, particularly for the stimulation of tissue. The invention also relates to a suitable manufacturing process for the electode. Such electrodes are, as a rule, coated.
European published patent applications EP 117 972 A, EP 116 280 A, and EP 115 778 A disclose electrodes for medical applications which have porous coatings of titanium nitride.
According to European Patent EP 0 054 781, a heart pacemaker electrode with low stimulation power is prepared which has a coating of platinum, indium, or a platinum-iridium alloy containing up to 20% by weight of iridium. The coating is performed galvanically in the examples.
According to J. Riedmüller et al., Proceedings of the 14th annual conference of the IEEE/EMBS, pp. 2364-2365, Orlando (1992), the surface of the coating is increased in order to achieve a higher capacitance and thus to decrease the impedance of the transition from the electrode to the cell. The surface area can thereby be increased, either by applying platinum-iridium spheroids and sintering them, or by coating a smooth surface with platinum black. As another alternative, iridium can be applied using a sputter technique.
From German Patent DE 42 07 368, a heart pacemaker electrode is known with a fractally sputtered iridium and Ir/Pt alloy coating. Iridium oxidizes during normal use to IrO2. Particularly for neurological applications, in which an excitation of significantly higher frequency than that of cardiological stimulation is used, this represents a significant problem, since the conversion of Ir to IrO2 can result in a degradation and dissolution of a layer in the body.
Furthermore, a platinum-black-coated electrode is known from U.S. Pat. No. 4,502,492. Platinum, as a noble metal, is on the one hand significantly more expensive than iridium. Moreover, however, the catalytic effect of platinum is more extensive, so that side effects may occur during contact with tissues.